Electbic besistance fttbitace adapted fob habpektihq by nitrooeinzatiakr



. A. FRY ELECTRIC RESISTANCE FURNACE ADAPTED FOR HARDENING BY NITROGENIZATION Nov. 18, 1930.

Original Filed Aug. 2; 1926 2 Sheets-Sheet l in B/{KB A. FRY 7 ELECTRIC RI8TSTANCB FURNACE ADAPTED FOR HARDENING BY'NITROGBNIZATION Nov. 18, 1930. Re. 17,874

Original Filed Aug. 2, 1926 2 Sheets-Sheet 2 Fig.3.

Reissued Nov. 18, 1930 UNITED STATES PATENT OFFICE ADOIJ' FRY, OF ESSEN-RUHB, GERMANY, ASSIGNOR, IBY MESNE ASSIGNMENTS, TO THE NITRALLOY CORPORATION, A CORPORATION OF DELAWARE ELECTRIC RESISTANCE FURNACE ADAPTED FOR HARDENING; BY NITROGENIZA'IION Original No. 1,861,694, dated March 6, 1928, Serial No. 126,650, filed August 2,19%, and in Germany I September 4, 1925. Application for reissue filed July 20, 1929. Serial No. 379,861.

The purpose of the invention isto provide an electrical resistance furnace for hardening metal articles by nitrogenization which is characterized by a simplicity of structure,

I and which can be disassembled to a large ex tent and attended in a very easy manner.

In order that the invention may be clearly comprehended, an example of one embodiment of the same will be described in detail with reference to the accompanying drawings which form a part of the specification. The embodiment herein illustrated discloses a resistance furnace operated by means of three phase current and designed to be used 1 for hardening steel articles by nitrogenization.

In the above mentioned drawings wherein like characters of reference designate like. parts throughout:

39 Fig. 1 is a. sectionalview taken longitudinally through the furnace;

Fig. 2 is a transverse section taken on the line 2-2 of Fig. 1; and

Fig. 3 is a diagrammatic view of the electrical connections employed in operating and maintaining the three phase current designed for use in connection with the present invention.

Referring to Figs. 1 and 2, the reference character A designatesthe brickwork of the furnace, and into the foundation of thisbrickwork a plurality of illar blocks B of refractory material are uilt. These blocks B form supports for a box D which is rectangu- 5 lar in cross section and open at its ends' and which rests on the blocks B by means of cross carriers C. The box D is made of a heat andcorrosion-proof alloy. As a result of considerable research and experiment, it

' has been found that an alloy of chromium,

. nickel and iron is best adapted to perform the desired requirements; this alloy will be commonly referred to in this specification as chromium nickel steel. A steel alloy that has been found to be particularly suitable for this purpose comprises in a representative analysis chromium about 25%, nickel'about 20%, silicon 0.8-1.0%, and carbon around 0.3%, the balance being principally iron. The box Dis provided on its outer surface with insulators (not shown) carrying the heatin resistance E, which is'subdivided so as to orm three hase windings. This resistance E is forme of chromium-nickel-iron wire. The windings are designated at E, E and E, and the ends of the same, as may be seen in Fig. 3, are led out of the furnace through its-wall and are so connected, by means of a four pole throw-over switch F, Fig. 3, to a three phase main G, that in the switch position denoted by Lstar connection is established, and in position 11 series connection is established.

By means 'of suitable screw bolts it the box D is suspended from cross carriers H which rest on-the side walls of the brickwork. The furnace is covered on the top by an iron cover plate J loosely. resting on the brickwork A and after the removal of this plate the box D sists of three rails K, which are U-shaped in cross section as maybe seen in Fig. 2. These rails are riveted to the floor of the box 'and each is provided with a guide rod Similar tracks K and K projecting into the box D through the front and rear openings of the furnace form prolongations of the tracks K, at both sides 0 the box, and are arranged together with the carriers H may be removed outside the furnace in the manner shown in i Fig. 1.

system of loose double rollers M is adapted to run on the rails K, K, K, said rollers being interconnected by axles m and lateral frame-plates m so as to form a moving plat form. The length of the whole roller system M, m m is about two and one-half times the length of the furnace.

.A receptacle P, adapted to receive the articles to be nitrogenized, is removably supported within the heatin I chamber formed by the box D. The receptac c has a bottom plate N which is supported on the loose rollers M, and suitable means, such as wire, ro e or the like, may be attached to the receptac e to permit removal of the same from the furnace. The receptacle P is closed in a gas-tight mannickel steel alloy having a particularly high resistance to heat and chemical influences. A

. pipe p for supplying nitrogen or a nitrogepenetrates the articles to 'm' which rests on v p and" 1) have nous s to the receptacle P passes through one o the end walls and extends nearly up to the opposite end wall thereof. A pipe p passing through the same end wall serves to lead ofi the gas- A second, similar receptacle R is shown as resting outside the furnace on that portion of the moving platform M, m, the track portion denoted by K The heating chamber of the furnace is closed to the outside atmosphere by loose 'walls Q which have to be removed before the receptacle Pis entered.

In actual operation when'the furnace, still empty but closed by the loose walls Q, has been heated up b connecting the resistances E, E E to the three phase main G with the throw-over switch F in position I (star connection) the switch F is turned over into position II, in which the base windings take only so much current as is suflicient to maintain the temperature attained by the heatingup operation- "The receptacle P which has been filled in the meantime with the articles to be hardened and closed in a gas-tight manner, is then entered, after removal of the loose walls Q, into the heating chamber of the furnace. When this takes place, the mov- 111g platform displaces itself with half the spee :the. rece tacle P. After the i s 0% 11 connected to a l fot tle containing the nitrogenous gas, the furnace is closed again by the loose walls Q. The nitrogenous gas is thereuponsupplied to the receptacle P heated by means of the resistances E, E, E 'During' this 0 ration nitrogenh: hardened and hardens them. During the period of nitrogenization the second receptacle R, is put on' the track portion K and filled with articles, to be hardened. As soon as a suflicient quantlty of nitrogen has been supplied to the articles contained in receptacle P and receptacle R has been filled, the loose walls Q are removed. The receptacle P is thereupon shifted in the direction of arrow 2:, Fig. 1. This motion is taken part in by the moving platform with half the speed, and by the rece tacle R with the speed of the receptacle When the receptacle R has reached the former position of the receptacle P, the latter, which now is outside the furnace, is brought to a standstill and the loose walls Q are brought into position again. Thisdone, the'articles contained in receptacle R are nitrogenized ,and receptacle P is emptied and refilled with articles to be hardened, so that it enters the furnace at the same time as the receptacle R leaves it. From this time the described operations may be repeated as often as desired. Whe'n' the furnaceis to'be shut down,

it is merely necessary to interrupt the current supply to throw the entire device out of operatlon.

D is capable of receivin a shiftable rece tacle enables a great num r of articles to treated at the same time. and in a very easy manner. In comparison with receptacles The fact that the electrically heated body V running on wheels the arrangement of the receptacles P and R on the described roller system offers the very important advantage of the pulling in and out of the filled receptacles taking place in a very easy manner.

ing nitrogenwhich is caused bycontact there-' of with the heated materials customarily employed in forming the walls of heating furnaces of this .type, is prevented. Metals or metal alloys of this kind are called herein metals having the properties of chromium nickel steel. Another 1m rtant feature of the invention is the extension of the gas supply pipe nearly to the opposite end wall of the receptacle p, p. The enables the gases entering the furnace to be gradually heated.

so that when they finally contact with the articles to be treated they have reached a preheated condition corresponding to the treatin temperature desire he provision of removable covers for the receptacles offers the advantage, in comparison with the front wall closures heretofore 'used with resistance furnaces, that the articles. to be treated maybe more easily intro entation of steelor, in fact, forperforming- It is to be distinctly understood that variany kind of heat treatment of iron, steel or other metal articles.

I claim:

1. In an electric resistance furnace adapted for hardening metals by nitrogenization, a roller system, a nitr'ogenizing rece tacle mounted thereon, and a removable e ectrically heated casing surrounding said receptacle and enclosing a portion of the roller system. j

2. In an electric resistance furnace adaptedfor hardening metals by nitrogenization,

a nitrogenizing reczptacle movably mounted in the furnace, an ec't'rically heated 105 duced to and withdrawn from the furnacgat surrounding said receptacle,means extending through a major portion of the length of the v furnace for assing a nitrogenous gas in heat- I I absorbin re ation to said casing and recepta- 5' cle and t en delivering the same in a heated condition to the interior of said receptacle, and means for with drawin residual ases from said rece tacle at 'a pomt remote m I thepoint of de ivery thereto. m 3. In an electric resistance furnace adapted for hardening metals by nitroge-nization, a roller system, a nitrogenizing receptacle formed of a metal having the roperties of chromium nickel steel as regar s decom si- 15 tion of nitrogeneous gases contacted t ere- I with at nitrogenizing temperatures mounted thereon, an electricall heated casing surroundin said recepta e and enclosing a portion of t e roller system. m 4. In a furnace for hardening metals by nitrouienization, a nitrogenizing rece acle mov ly mounted in the furnace a pipe exthrough one wall of sai rece tacle to a pomt adjacent the opposite wall or introducing nitrogen, and means for leading.' residual gases from said receptacle throng an opening in said first-mentioned wall. Signed at Cologne, Germany, this 6th day I of July,1929.

'80 ADOLF FRY. 

